In the printing industry, a desired image is repeatedly printed on a continuous web or substrate such as paper. The ink is dried by running the web through curing ovens. In a typical printing process, the web is subsequently slit (in the longitudinal direction which is the direction of web movement) to produce a plurality of continuous ribbons. The ribbons are aligned one on top of the other, folded longitudinally, and then cut laterally to produce a plurality of multi-paged, approximately page-length web segments, termed "signatures". A signature can also be one printed sheet of paper that has or has not been folded. It is often desirable to transport successive signatures in different directions. In general, a sheet diverter operates to route a signature along a desired one of a plurality of paths.
U.S. Pat. No. 4,373,713 discloses a pair of rotary diverters (62, 63) having cam surfaces which divert successive signatures alternately to opposite sides of a diverter wedge (23). After passing the wedge, the signatures are engaged by a belt system, comprising inner belts (25, 26) and outer belts (12, 13), that transport the signatures to the next operation.
Similarly, U.S. Pat. No. 4,729,282 discloses a sheet diverter including an oscillating diverter guide member that directs successive signatures to opposite sides of a diverter wedge.
A sheet diverter in a folder at the end of a printing press line must be operable at the high speeds of the press line, typically in excess of 2,000 feet per minute (fpm). It is desirable to run both the press and folder at the highest speed possible in order to produce as many printed products as possible in a given amount of time. However, the physical qualities of paper or similar flexible substrates moving at a too high rate of speed often results in whipping, dog-earring, tearing, or bunching of the substrate. For example, the sudden impact force between the leading edge of a signature and the diverter wedge may result in the leading edge of the signature being damaged. Similarly, the trailing edge of a signature may slap against the top vertex edge of the diverter wedge, resulting in damage to the trailing edge. The trailing edge of the signature may tear, or be unintentionally folded on the corners. Damaged signatures may be of unacceptable quality and may also lead to jams in the folder, resulting in downtime and repair expense.
Additionally, the ink on a printed signature can be smeared, smudged, or offset to the wedge when the signature strikes the diverter wedge at a high rate of speed. Ink offset on the diverter wedge can also cause undesired smudges on successive signatures.
Many of these defects become more prevalent above certain speeds of the printing press and folder. For example, such defects may occur when the press is run at 2300 fpm, but may not occur when the press is run at 2200 fpm.